This invention relates to batteries.
Batteries, such as alkaline batteries, are commonly used as energy sources. Generally, alkaline batteries include a cathode, an anode, a separator, and an electrolytic solution. The cathode is typically formed of an active material (e.g., manganese dioxide), carbon particles, and a binder. The anode can be a gel including an active material (e.g., zinc particles). The separator is usually disposed between the cathode and the anode. The electrolytic solution, which is dispersed throughout the battery, can be a hydroxide solution.
Alkaline batteries include the conventional AA, AAA, AAAA, C, and D batteries commonly sold in stores. These conventional alkaline batteries include a cylindrical container containing a central, cylindrical zinc gel anode surrounded by a ring-shaped manganese dioxide cathode.
It generally is desirable for a battery to have a long service life. One measure of the service life of a battery is the length of time the battery can discharge under a given load before the voltage drops to an unacceptable level.
The invention relates to a battery having an increased service life when discharged continuously, for example, at 1 amp.
In one aspect, the invention features a battery having a housing, a first electrode within the housing, a second electrode within the first electrode, and a separator between the first electrode and the second electrode. The second electrode is non-cylindrical provides an increased interface area between the first electrode and the second electrode. Because the second electrode is non-cylindrical, it has surface bounded by a first circle of radius r1 and a second circle of radius r2. Preferably, the inner radius is less than 90% of r1, more preferably less than 70% of r1, and most preferably less than 60% of r1.
In preferred embodiments, the circumference of the second electrode may be curvalinear (i.e., formed, bounded, or characterized at least in part by curved lines); the first electrode may be a cathode including manganese dioxide; the second electrode may be an anode including zinc; the housing may be cylindrical; and the second electrode includes two, three, or four lobes. The battery may be, for example, an AA, AAA, AAAA, C or D battery.
The service performance of a battery also depends on the efficiency with which the battery uses the active material of the anode and the cathode during discharge. Another aspect of the invention relates to a battery including a first electrode and a second electrode having a plurality of lobes. A first lobe has a first generally linear side portion that is a distance d1 from a side portion (preferably a generally linear side portion) of an adjacent lobe. The first lobe is a minimum distance d2 from the housing, and the ratio d1:d2 for the first lobe is between 1.5:1 and 2.5:1. Maintaining a d1:d2 ratio of between 1.5:1 and 2.5:1 enhances the efficiency with which the battery uses the active materials because the cathode material between the first lobe and the adjacent second lobe will be consumed at approximately twice the rate as the cathode material between the first lobe and the housing. Preferably, the ratio d1:d2 is between 1.7:1 and 2.3:1, more preferably between 1.8:1 and 2.2:1, and most preferably between 1.9:1 and 2.1:1.
In preferred embodiments, the first lobe also has a second generally linear side portion that also is the distance d1 from another side portion (preferably a generally linear side portion) of an adjacent lobe. In addition, the lobe including the generally parallel side portion also is a minimum distance d2 from the housing.
The minimum distance (d1) can be measured at any position along the length of the battery by determining the minimum distance between the surface of the first electrode adjacent the halfway point of the generally linear side portion of the first lobe and a surface of the first electrode adjacent the halfway point of the side portion of the adjacent lobe. The minimum distance (d2) is measured at the same position along the length of the battery by determining the minimum distance between a surface of the first electrode adjacent the lobe and a surface of the first electrode adjacent the housing. For example, d1 and d2 can be measured at the halfway point along the length of the battery, or one third of the way along the length of the battery, or two thirds of the way along the length of the battery. In some embodiments, the ratio d1:d2 is the average ratio d1:d2 along the length of the battery.
Other features and advantages of the invention will be apparent from the description of the preferred embodiments thereof, and from the claims.